Of course, having civilians travel with soldiers, and indeed go to the battlefields with them, was the norm until very recently.

What changed? For one thing, lives grew longer and people apparently began fearing death more. But that's not a decisive factor: even in the modern times, civilians practice war tourism, deliberately seeking battle where they have no means of defending themselves, simply because that's exciting.

More importantly, armies no longer needed civilians. After millennia of misery, there finally existed means of bringing food and water to the front lines. Troops could be rotated, whorehouses could be safely placed dozens of kilometers away from the battle sites, and even families left overseas could be visited. Wars became longer, too: instead of the lads fighting until the harvest season and then going home (possibly to continue in the spring), armies were maintained for several years in a row. Means coincided with necessity, and suddenly there emerged a homefront. Until it went away and war came back to the middle of civilian life, with air power and then with ICBMs.

The Trek future, no matter its exact specs or the pseudohistory that led to those specs, would be a post-homefront future, possibly many times over. It would include awareness of the futility of homefronts, if not at that specific point in history, then in history in general. Staying home when a family member takes risks might simply no longer be considered particularly worthwhile, all things considered.